sedimentary
Glauconite (Green Sandstone)
Glauconite (K,Na)(Fe,Al,Mg)2(Si,Al)4O10(OH)2
Hardness: 2 Mohs; Color: Dull green, olive green, or blue-green; Luster: Dull to earthy; Crystal structure: Monoclinic (micaceous); Cleavage: Perfect basal; Specific gravity: 2.4-2.9.
- Hardness
- 2 Mohs
- Color
- Dull green, olive green, or blue-green
- Luster
- Dull to earthy
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Physical properties
Hardness: 2 Mohs; Color: Dull green, olive green, or blue-green; Luster: Dull to earthy; Crystal structure: Monoclinic (micaceous); Cleavage: Perfect basal; Specific gravity: 2.4-2.9.
Formation & geological history
Formed in marine environments through the alteration of minerals like biotite or fecal pellets in shallow continental shelf waters. Often found in Cretaceous and Tertiary seafloor deposits.
Uses & applications
Used historically as a green pigment for paint, as a water softener due to ion-exchange properties, and widely used today as a natural slow-release organic fertilizer.
Geological facts
Glauconite is an indicator of slow sedimentation rates in marine environments. When it is found in high concentrations, the rock is often called a 'Greensand'.
Field identification & locations
Identify in the field by its distinctive green color and crumbly, sandy texture. It usually occurs as small rounded pellets or grains within a sandstone or clay matrix. Found heavily in the Atlantic Coastal Plain of the USA.
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